In general, plasma refers to an ionized gas state of matter formed of ions, electrons, radicals, or the like. Plasma may be generated by heating a gas to a very high temperature or subjecting a gas to a strong electromagnetic field or a high-frequency electromagnetic field.
A plasma treatment apparatus refers to an apparatus allowing a reactive material to be in a plasma state so that the reactive material in the plasma state may be deposited on a semiconductor substrate, or allowing a semiconductor substrate to be washed, ashed, or etched using a reactive material in a plasma state. The plasma treatment apparatus includes a lower electrode installed inside a chamber to mount a substrate thereon, and an upper electrode installed in an upper portion of the chamber to oppose the lower electrode.
In order to precisely control a plasma treatment process, it is important to be able to accurately monitor the state of plasma during the process. Thus, research into techniques of monitoring the state of plasma used in plasma treatment processes has continued.